At night, repairs underway to stabilize slabs on I-78

Q: Attending the great plays and musicals at DeSales University sometimes puts us on Route 78 around 11 p.m. Recently on those trips we've run into long construction delays. What are they doing? I have never seen road work like this. They cut out a small, square section of the road surface, and by the next day it is covered again. The only guess I have is that they are installing a de-icing system. Can you explain this very usual work?

— Denise Lesko, Bethlehem Township

A: Automatic chemical-spray systems using nozzles mounted at the roadside are in use, particularly in some of our more icy climbs, though I know of no examples in our region, Denise. Good guess, but that's not the basis for the work you've seen on I-78.

Rather, the nighttime work — little pat on PennDOT's back for that choice, by the way — is part of the continuing effort to extend the life of the 24-year-old roadway. Similar rehab work was done on a smaller section of the interstate in 2008, and though the method might appear to be madness, it seems to work.

The intriguing part to my engine control module is the technology employed in dealing with the problem of sinking, loose or shifting concrete slabs that make up the highway. Workers drill holes in a sunken slab, down to the point where the slab rests on the crushed-stone surface, or base. They insert a hose and inject a liquid urethane material in the void between slab and base. Like retail building-insulation foams used by homeowners, the urethane expands as it dries, but with enough force to lift an entire highway slab.

The problem slab thus restored to the level of its neighbors, it is stabilized using epoxy-coated steel reinforcing bars dropped into slots cut into the road surface and secured with new concrete. Groups of these bars together act as "cages" that spread the force of the traffic load between slabs, helping to hold everything together.

In today's photo, the short "dash" lines at the seams in the road surface mark areas where these "load transfer units" were put in during the 2008 renovations, in this case on eastbound 78 approaching the Cedar Crest Boulevard exit. The red markings on the roadway indicate cracking, spalling or otherwise deteriorating sections of the surface that will be repaired when the contractor arrives at this section, said PennDOT engineer John Harmonosky.

I wondered whether that was an indication the slab stabilization done five years ago was failing, but Harmonosky said the slabs in the area I photographed do not need re-stabilization, as it were; rather, the red markings specify locations where the surface deterioration unrelated to sinking slabs has occurred. A closer look at my photographs seemed to bear this out; many of the markings surround small holes or "pitting" in the concrete, or vertical cracking, in slabs that do not have the telltale "dash" lines from the 2008 work.

"Most of [the deterioration] we marked out happened at new locations" and is not related to the previously stabilized slabs, he said. "As you know, this is a heavily traveled roadway with heavy truck traffic." I certainly had no argument there.

In some cases, slab deterioration precludes the use of any stabilization and repair techniques, and the whole rectangular hunk of concrete has to be replaced, Harmonosky said. One such case stands out because of its fresh, white color and perfect surface on the westbound side approaching the Lehigh Street exit.

Examining the road surface and the paint markings got me to wondering when the surveys are done to determine which areas need attention, and are marked. I couldn't imagine anyone being able to examine the road surface and spray the paint for the markings by running onto the travel lanes and quickly escaping before traffic arrived. Even at off-peak daytime periods, volume is far too heavy.

That work generally is done at night as well, Harmonosky said, and some of it continues while the repairs are being done, with specified lanes conveniently closed to accommodate the work.

PennDOT spokesman Ron Young said the $2.15 million slab stabilization, concrete patching, and joint-sealing/cleaning contract secured by J.D. Eckman Inc. of Atglen, Chester County, covers about a 15-mile section of the interstate roughly between the Route 22 split and Hellertown. They've mostly been limited to Monday through Thursday nights, though some weekend work has been done, which may be what you've encountered, Denise.

The contract was awarded last September, and the job "should be done by the end of August, if not sooner," Young said.

Road Service: Starting Tuesday, Dauphin Street in Allentown will be closed between Long Drive and American Parkway, and remain so for the next two months for work related to the completion of American Parkway. Long Drive, just north of Union Boulevard, is the access road to the parking area for Coca-Cola Park. Dauphin will be closed just north of Long, and just south of American Parkway. The closed portion normally provides access to Airport Road and Route 22, and to Catasauqua and other points north. The closure will put more traffic onto detour routes Union Boulevard, Airport Road and American Parkway.

Road Warrior appears Mondays and Fridays, and the Warrior blogs at mcall.com. Email questions about roadways, traffic and transportation, with your name and the municipality where you live, to hartzell@mcall.com, or write to Road Warrior, Box 1260, Allentown, PA 18105-1260.